The field of the invention is junction field-effect transistors and particularly junction field-effect transistors having a channel of the same conductivity type material as the source and drain electrodes.
A conventional junction field-effect transistor (JFET) comprises a source and drain electrode of a first conductivity type material interconnecting a channel of the same conductivity type material through which current flows. Contacting the channel and forming a junction therewith is one or more gate regions of a conductivity type material opposite to that of the channel. If used in an integrated circuit the JFET is normally mounted on a semiconductor substrate and the JFET is isolated from other devices with an isolation region, of semiconductor material of a conductivity type opposite to the gate, which surrounds the JFET.
Reverse biasing the gate and channel junctions causes depletion regions to form in the channel. Current flow through the channel is controlled through the use of these depletion regions which, when merged, pinch off current flow through the channel and, when unmerged, allow current to flow.
Since the source and drain electrodes are of a different conductivity type material than the gate electrode, metal interconnects must be used when interconnecting conventional JFET devices. In conventional devices gate electrodes must also be isolated from the substrate if they are to be useful in integrated circuits. In addition conventional construction has prevented enhancement mode junction field-effect transistors from being realized, that is, a device whose channel current is zero with the gate and source electrodes connected together.
The use of merged depletion regions has had limited uses in the prior art. When merged, the same potential has been applied across opposing junctions and used for isolation, to achieve variable capacitance and to control current in the channel of a junction field-effect transistor where the depletion regions pinch off current flow through the channel and thus control current through the channel. Until now, the merging of depletion regions other than in the channel of a JFET has been something that generally has been avoided due to the high currents that result when one of such regions inadvertently extends to the next junction and causes "punch through", that is, when one junction depletion region punches through to an adjoining junction with a resulting high current. Punch through, however, has been used intentionally for MOS input protection and as a noncritical voltage regulator.
Finally, Warner U.S. Pat. No. 3,404,295 uses a buried locklayer in a bipolar transistor, a region of conductivity type material of a type opposite to the collector buried in the collector, to prevent punch through of the emitter junction depletion region to the collector of the bipolar transistor. With a control voltage applied to the locklayer the collection of free carriers in the bipolar transistor can also be affected which affects the current flow through the bipolar device.